The present invention relates generally to metallic deposition materials and processes, and more specifically to materials and processes for metallic electroless deposition.
Metallic diffusion and/or drift between different metallic layers, or metallic and semiconductor layers induce changes over time in the properties of the layer into which diffusion and/or drift has occurred. These properties include electrical, mechanical, thermal, visual, physical and chemical properties. There is great importance to many industries to produce products having both constant properties over time and high reliability. These industries include, but are not limited to semiconductor, microelectronics, electro-finishing, aeronautic, space and motor industries. Products requiring high reliability include, for example, semiconductor chips, ULSI products, jewelry, nuts and bolts, and airplane wings and car parts. Typically, the smaller the product, the more pronounced an effect of a localized change in a property of a layer.
In the semiconductor industry, the diffusion of metals into adjacent layers is well documented. For example, copper diffuses into silicon materials. To prevent such diffusion, a barrier layer between the copper and silicon may be deposited (U.S. Pat. No. 5,695,810 to Dubin et al.)
The microelectronics industry constantly aims to reduce the size of components and the distance between interconnects, yet, simultaneously, tries to increase the number of electronic features per unit area. Thus, there is an increasing requirement for more accurate and well-controlled metal deposition techniques. For example, with decreasing size of copper/SiO2 interconnects, standard processes known in the art for metal deposition cannot typically meet the new requirements for precision. There is therefore an urgent need for better designed processes, materials and manufacturing methods for metal deposition.
One of the concerns in manufacturing and processing copper, amongst other metals, is its corrosion, before and after Chemical-Mechanical Polishing (CMP), which may induce deterioration in the electrical and mechanical properties of the copper. Another concern is the migration of copper onto the inter-level dielectric and the silicon substrate. Copper contamination in inter-level dielectrics weakens the dielectrics"" mechanical properties and reduces electrical reliability. Copper is also a deep level dopant in silicon, which may lower the minority carriers lifetime and may enhance leakage currents to significant levels.
Copper has poor adhesion to most dielectrics that are used in ULSI manufacturing, such as, but not limited to, SiO2, SiOF, polyimide and low-K dielectrics. Therefore, the implementation of a copper encapsulation method is desirable. One possible solution is to wrap the Cu lines with special thin metallic cladding that serves as a. a corrosion resistance layer; b. a diffusion barrier; and c. adhesion promoter.
There are many materials that are known to be good barrier diffusion. Usually they are refractory metals, such as Ta, W and Mo, or refractory metal nitride thin films such as TiN, TaN, and WxNy. The layers can be deposited by conventional physical vapor deposition (PVD), chemical vapor deposition (CVD) or Atomic Layer Chemical Vapor Deposition (ALCVD).
Alternative methods for barriers are electroplating and electroless (autocatalytic) deposition of Co- or Ni-based alloys. For example, it was shown that 100 nm thick electroless Coxe2x80x94P functions as barrier against Cu diffusion at temperatures of up to 400xc2x0 C. Addition of a refractory metal (e.g. W, Mo, or Re) ion to Coxe2x80x94P alloy improves its barrier properties significantly and 30 nm Co88W2P10 holds against copper diffusion at temperatures up to 500xc2x0 C.
Commonly used solutions for wet deposition of cobalt and nickel thin films contain alkali metal ions such as sodium or potassium. For example, conventional bath compositions for electroless deposition of Co(P,W) and Ni(P,W) layers include tri-sodium citrate as complexing agent, sodium tungstate as a source for W, sodium hypophosphite as a reducing agent, and sodium or potassium hydroxides to adjust the pH of the solution.
Alkali metal ions have many negative effects on the performance of CMOS integrated circuits. Sodium and potassium ions migrate rapidly under electric field in inter-level oxide, field oxide and gate oxide. The alkali metal ions degrade the dielectric strength of SiO2 by increasing leakage current and decreasing breakdown field. The effect of alkali metal ions is also very pronounced in transistor technologies that their characteristics depend on the electric field at the Si/SiO2 interface. Since alkali metal ions are very mobile in SiO2 the effective charge""s position in the silicon dioxide may vary under the applied electric field at normal circuit operation. This shift in the charge distribution centroid affects the internal electric field distribution and may causes long-term instabilities.
There is therefore an urgent need to develop novel materials and methods for metallic deposition which overcome the diffusion, drift and migration of metallic ions, in particular, alkali metal ions, between layers.
It is an object of some aspects of the present invention to provide improved materials and processes for providing a barrier layer for metallic layers, such as copper.
In preferred embodiments of the present invention, improved materials and processes are provided for the electroless deposition of cobalt tungsten phosphorus, substantially devoid of alkali metal ions and alkaline earth metal ions.
In other preferred embodiments of the present invention, methods and materials for activating a non-metallic surface for electroless deposition thereupon of cobalt tungsten phosphorus, substantially devoid of alkali metal ions and alkaline earth metal ions, are provided.
In further preferred embodiments of the present invention, methods and materials for activating a metallic surface for electroless deposition thereupon of cobalt tungsten phosphorus, substantially in the absence of alkali metal ions and alkaline earth metal ions, are provided.
In further preferred embodiments of the present invention, methods and materials for electroless deposition of cobalt tungsten phosphorus, substantially devoid of alkali metal ions and alkaline earth metal ions, on a single silicon crystal, on a thermal oxide on silicon, and on thin films of copper and cobalt on silicon substrates are provided.
In yet further preferred embodiments of the present invention metallic deposits of cobalt phosphorus and cobalt tungsten phosphorus are provided, wherein the deposits are substantially alkali metal free, alkaline earth metal free and oxygen free.
In still further preferred embodiments of the present invention, metallic thin films of cobalt phosphorus and cobalt tungsten phosphorus are provided, wherein the films are substantially alkali metal free, alkaline earth metal free and oxygen free.
There is thus provided in accordance with a preferred embodiment of the present invention, an aqueous composition for the electroless deposition of cobalt tungsten phosphorus, including;
at least one cobalt ion;
at least one tungsten containing ion; and
a reducing agent comprising at least one phosphorus atom; and,
wherein the composition is substantially devoid of alkali metal ions and alkaline earth metal ions.
In a preferred embodiment of the invention, the at least one cobalt ion is provided by cobalt sulfate heptahydrate (CoSC4.7H2O). Preferably, the cobalt sulfate septahydrate (CoSO4.7H2O) is present at a concentration of 10-25 g/l. Yet more preferably, the cobalt sulfate septahydrate (CoSO4.7H2O) is present at a concentration of 15-18 g/l. In another preferred embodiment of the invention, the cobalt ion is provided in the form of cobalt chloride hexahydrate (CoCl2.6H2O) in a concentration of 10-40 g/l.
In a preferred embodiment, the at least one tungsten containing ion is provided by at least one of the group of tungsten trioxide (WO3) and tungsten-phosphoric acid (H3[P(W3O10)]4).
Preferably, the tungsten trioxide (WO3) is present at a concentration of 0-7 g/l. Preferably, the tungsten-phosphoric acid (H3[P(W3O10)]4) is present at a concentration of 0-60 g/l, alone or together with WO3.
Preferably, the reducing agent is selected from ammonium hypophosphoric acid (NH4H2PO2) and hypophosphoric acid (H3PO2). Preferably, the ammonium hypophosphoric acid (NH4H2PO2) is present at a concentration of 10-30 g/l, more preferably, the ammonium hypophosphoric acid (NH4H2PO2) is present at a concentration of 12-25 g/l, and most preferably, the ammonium hypophosphoric acid (NH4H2PO2) is present at a concentration of 15-20 g/l.
In a preferred embodiment of the invention, the composition further comprises a complexing agent. Preferably, the complexing agent includes triammonium citrate ([NH4)3C6H4O7). More preferably, the triammonium citrate is present at a concentration of 40-60 g/l.
In a further preferred embodiment, the composition further includes a surfactant. Preferably, the surfactant includes at least one of RE-610 and Triton X-100.
In a preferred embodiment of the present invention, a cobalt tungsten phosphorus film is deposited on a surface from a bath comprising any of the aforementioned bath compositions. Preferably, the film has a thickness of less than approximately one micron. More preferably, the film thickness is less than approximately 0.1 micron.
In a preferred embodiment of the present invention, the film has a resistivity of less than 100 microOhm.cm. More preferably, the resistivity of said film is less than 50 microOhm.cm.
In another preferred embodiment of the present invention, the film comprises 0-12% phosphorus.
In a further preferred embodiment of the present invention, the film comprises 0-6% tungsten.
In yet another preferred embodiment of the present invention, the film comprises at least 85% cobalt.
In a still further preferred embodiment of the present invention, the film acts as a diffusion barrier for a metal on the surface, wherein the metal is selected from copper, gold, platinum, palladium, silver, nickel, cadmium, indium and aluminum.
Preferably, the film is substantially free of alkali earth metals and alkali metals.
Preferably, the film is substantially oxygen-free. Preferably, the film acts as an oxidation barrier. Additionally or alternatively the film acts as a corrosion barrier.
There is also provided in accordance with another preferred embodiment of the present invention, a method for the electroless deposition of cobalt tungsten phosphorus on a surface, including;
electrolessly depositing cobalt tungsten phosphorus on the surface, substantially in the absence of alkali metal ions and alkaline earth metal ions.
In a preferred embodiment of the present invention, the method further comprises activating the surface, and wherein activating the surface occurs at least partially under dry process conditions. Preferably, the surface comprises silicon. Additionally or alternatively, the surface comprises cobalt. Additionally or alternatively, the surface comprises copper.
In a further embodiment, activating the surface further comprises depositing at least one metal on the surface. Preferably, the at least one metal is selected from aluminum, cobalt, copper and titanium.
In a further preferred embodiment, the method further comprises removing at least partially some of the at least one metal.
In yet another preferred embodiment of the present invention, activating the surface occurs, at least partially, under wet process conditions.
In a preferred embodiment of the present invention, activating the surface comprises at least one of the following steps;
(a) degreasing the surface;
(b) removing at least one oxide from the surface;
(c) fluoride etching the surface;
(d) rinsing the surface;
(e) activating the surface with palladium; and
(f) pre-dipping the surface in a solution comprising at least one of a reducing agent and a complexing agent.
Preferably, the surface includes at least one of silicon, cobalt and copper.
In a further preferred embodiment, the method includes depositing a film of the cobalt tungsten phosphorus on the surface. Preferably, the thickness of the film is less than approximately one micron, and more preferably the film thickness is less than approximately 0.1 micron.
In a preferred embodiment of the present invention, the film has a resistivity of less than 100 microOhm.cm. More preferably, the resistivity is less than 50 microOhm.cm.
In a preferred embodiment of the present invention, the method provides a film including 0-12 % phosphorus.
In another preferred embodiment of the present invention, the method provides a film including 1-6% tungsten.
In yet another preferred embodiment of the present invention, the method provides a film including at least 85% cobalt.
In still another preferred embodiment of the present invention, the method includes depositing the cobalt tungsten phosphorus at a temperature of around 70xc2x0 C. up to 100xc2x0 C. More preferably, the temperature is at least 80xc2x0 C.
In yet another preferred embodiment of the present invention, the method includes depositing the tungsten phosphorus at a pH of around 8 up to about 12. More preferably, the pH is from around 9 up to about 11.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: